Computed tomographic scanners are well known in the art and have evolved over time. In general, they may be classified based upon their scanning technique and the geometric relationships between the X-ray source and the detectors.
Early scanners used a "translate-and-rotate" technique, where multiple independent pencil beams of X-rays emerged from a collimator and impinged on an array of detectors. In use, the X-ray tube and detector array are linked together and move as a single unit in a linear "translation direction". Next the entire assembly would be rotated a few degrees and translated again. The collection of scan data was very time consuming with this structure, due to the complex mechanical motion of the system.
Next "rotating-source/rotating-detector" systems were developed. In these systems the X-ray source and detector array are linked together and rotate about the patients body. More recently systems have been developed in which only the X-ray tube moves illuminating a large stationary array of detectors.
Each of these approaches involves compromises in terms of cost, complexity and scan time. In general it is desirable to complete a scan as rapidly as possible to reduce the deleterious effects of patient motion and to reduce the overall dosage of x-rays.